Field of the Invention
Embodiments described herein relate to power management and particularly to more effective use of idle states.
Description of the Related Art
Reducing power consumption and extending battery life are ongoing goals of electronic system design. The Advanced Configuration and Power Interface (ACPI) specification is an industry standard that defines common interfaces for power management and gives the operating system (OS) control of power management. For microprocessors, ACPI-based low-power states have been employed to reduce power consumption. The ACPI standard specifies various groups of states, among them global states, device states, performance states, and processor states. The ACPI standard defines four processor power states, C0-C3. C0 is the operating state. In state C1 the processor is halted and does not execute instructions, but can instantaneously return to an executing state. In state C2 the processor stops clocks but maintains cache contents and all software-visible state data, and services cache coherency probes. Finally, in state C3 (a Sleep state), the processor maintains cache contents and software state, but lowers voltage to a level sufficient to maintain the saved state. While these power states have been useful in helping save power, additional power savings remains a focus of system goals, particularly for battery powered systems.